The present invention relates to an extendable hinge, and more particularly a hinge for spectacles.
Known extendable or spring hinges usually incorporate two rigid parts whose adjoining ends have a matching configuration and may include an external surface producing a cam action on the bearing faces, which parts are hinged to each other about a point of pivoting and connected to each other by a helical compression spring whose function is to return the rigid parts towards each other and keep these parts in one or more stable positions. When fitted to, say, a spectacle frame, hinges of the abovementioned type sometimes allow extended opening of the sidepieces beyond the stable open position (in which the sidepieces form an angle of approximately 93xc2x0 with the front face of the frame) in such a way as to facilitate the placing of the frame on the wearer""s face.
In recent years much research on hinges of this type has been targeted at reducing their size as far as possible, particularly in terms of their height, in order to enable them to be built into the increasingly lightweight frames now found on the market. This research has led to the springs being miniaturized, which, although giving satisfactory results, has by now reached a limit, the reduction in the size of the turns being limited by the diameter of the spindle around which they must sit.
Recent developments in spring hinges have therefore led to helical springs being replaced by a leaf of an elastic material such as polyurethane, or by a leaf spring. Progress in terms of size has however been insignificant because the reduction in size of these hinges is necessarily accompanied by a decrease in the height of the bearing faces of the rigid parts, thus resulting in enormous wear which makes it impossible to guarantee reliable operation of the hinge.
For example, patent application EP-A-0,115,826 discloses a spring hinge for a spectacle sidepiece in which the sidepiece is connected to a socket that pivots, about a screw, on a head forming a cam which is itself integral with the front face of the frame. The socket contains a leaf spring consisting of a stack of three diamond-shaped leaves held in place by fixing one of its ends in the socket while its other end is intended to press against either of two perpendicular surfaces of the said cam in order to define two stable positions, namely open and closed, of the sidepiece. The hinge disclosed also allows slightly extended opening of the sidepiece which is limited by stop means. A device working on the same principle is disclosed in EP-A-0,235,780. This device additionally incorporates a screw for adjusting the initial tension of the spring, which in this patent application has a circular cross section with frustoconical ends.
In these two known devices, the cam head has such small bearing surfaces that the device cannot, without deformation, take stresses very slightly greater than those which it undergoes normally in the course of use, particularly stresses applied at right angles to the normal plane of articulation of the hinge, unless the height of the cam part is increasedxe2x80x94the very opposite of what is intended. Also, these devices require adjustment screws and/or fastening screws. Consequently the known spring hinges which use leaf springs are unsuited to the stresses currently imposed in the spectacles market both by manufacturers, as regards the minimum load the frames must be able to withstand without deforming, and by users concerned about the aesthetic appearance of the frames.
French Patent No. 1,593,112 in the name of Mari discloses a click-action hinge for a spectacle frame that comprises a square-section spindle about which can pivot a sharp-edged seat mounted in a spectacle sidepiece. The sidepiece has two stable positions. In addition, the seat has a longitudinal slot which gives it a certain elasticity and allows elastic return of the sidepiece to the normal open position after it has been opened slightly past the perpendicular to the face.
The known hinge does not have the disadvantages of the devices mentioned earlier. However, it requires, by its very design, a gap between the sidepiece and the front face of the frame, and dirt can settle in this gap. The gap is also aesthetically unattractive, as is the visible seat. In addition, a slight tug on the sidepiece in the direction of the wearer""s ear is sufficient to pull the hinge apart. Lastly, the elastic return to the open position has to overcome friction forcesxe2x80x94which themselves cause hinge wearxe2x80x94exerted by the seat on the square-section spindle and, because of the configuration of the spindle, this action can, beyond a certain angle of pivoting of the sidepiece, take the sidepiece as far as a position lying in the continuation of the face of the frame.
The Object of the invention is therefore to overcome the disadvantages of the prior art.
More specifically, it is an object of the invention to provide a novel extendable hinge that is extremely small, particularly in terms of height, but nonetheless does not impair the ability of the said hinge to withstand breakage, particularly during the application of stresses perpendicular to its normal plane of articulation or under the action of a tensile force acting along the sidepiece.
Another object of the invention is to provide an extendable hinge that has no visible screws or connecting and/or return parts.
Another object of the invention is to provide an extendable hinge whose manufacturing costs are less than those of hinges of the prior art.
These objects are achieved by the present invention in that it provides a hinge comprising, in a manner known per se, a first rigid part mounted so as to pivot about a pin on a second rigid part, which first part contains spring means that consist of at least one leaf spring and are such as to engage with a part having a cam surface fixed to the said second part, or made in one piece with it, in order to define stable relative angular positions of the said rigid parts.
The hinge according to the invention differs from the known hinges, however, in that one end of the said first rigid part is connected to, or consists of, a portion forming a knuckle which is inserted between a pair of knuckles that form the end of the said second rigid part, with the said pin being inserted through all these knuckles, while a bush is interposed between one knuckle of the said second rigid part and the said pin, which bush defines both a cylindrical passage in which to accommodate the said pin and an external peripheral surface constituting the said cam surface and against which at least a portion, termed the xe2x80x9cclamping portionxe2x80x9d, of the said spring means is designed to fit.
The clamping portion of the spring means may be, for example, in the general shape of a Y or in the general shape of a flat hook. Furthermore, the spring means may be composed of a single leaf spring or several leaf springs that are superimposed and/or arranged side by side and oriented in such a way that their smallest dimension, in cross section, extends in a plane perpendicular to the normal plane of articulation of the two rigid parts. In order to reduce the size of the hinge to a minimum, the smallest dimension of the spring means will be, for example, approximately 0.4 mm, so as to give a hinge having a total height of no more than approximately 2 mm.
The stable relative angular positions of the rigid parts will preferably be obtained by engagement of at least one recess provided on the said cam surface with at least one matching protuberance provided on one end of the said clamping portion of the spring means. The number of protuberances and matching recesses, by which one rigid part is held in a stable position relative to the other, is not restrictive and will depend on the intended use of the hinge according to the invention. As a variant and/or in addition, the holding of the sidepiece in the open and closed positions could be produced instead by the bush being xe2x80x9csqueezedxe2x80x9d by the clamping portion of the spring means. If so, the recesses and protuberances would not necessarily match each other exactly.
In a first embodiment of the invention, the knuckle portion is formed by one end of the said first rigid part, in which case the spring means are preferably in the general shape of a Y whose two arms form the said clamping portion of the said spring means. Advantageously, the spring means also include a return part composed of a third arm, made in one piece with the said two arms and adjacent to these in the said normal plane of articulation, which third arm is such as to abut elastically against the said second rigid part.
In a second embodiment of the invention, the said knuckle portion of the first rigid part is formed by another portion, termed the xe2x80x9cencircling portionxe2x80x9d, of the spring means.
In this case the spring means advantageously also include a return part shaped like a flat hook having an outwardly curved tip that is such as to abut elastically against the said second rigid part. The return part may be a separate part which is placed on top of the said encircling portion of the said spring means. As a variant, it may be formed by a portion surrounding the encircling portion of the spring means, in the normal plane of articulation.
It will be understood that the special structure of the hinge according to the invention, particularly the engagement of the knuckles and the close fit of the clamping portion of the spring means around the bush, gives the hinge good resistance to the stresses which may be applied to it in several planes. It is obvious too that, because of the elimination of the bearing faces on the external surface of the second rigid part, the latter may advantageously be made from a commonly used material, such as nickel-silver or titanium, whereas more expensive materials capable of withstanding a large shearing force, such as treated steel, may be reserved for the bush described earlier.
The invention also relates to applications of the hinge described above. The hinge finds its most useful application as a spectacle frame hinge, in which one of the rigid parts is mounted on, or consists of, a spectacle sidepiece and the other part is a rigid component integral with the front face of the said spectacle frame, often known as a xe2x80x9ccorner piecexe2x80x9d. The hinge according to the invention may be used, in a variant, in the hinging of a door, such as a refrigerator door or a vehicle door, with respect to a door frame. However, these applications are not of course restrictive, and other types of articulation familiar to those skilled in the art can be fitted with the abovementioned hinge.